The invention relates to a method of connecting, without a visible seam, at least one basin deep-drawn from a metal sheet, to the basin opening of a frame consisting of sheet metal, for example, the basin opening of a cover plate formed from a stainless steel plate, of a kitchen sink unit or the like, by the employment of at least one welding process, wherein, starting from the upper edge of its vertical wall, the basin comprises a surrounding rim which is connected to said wall by an arcuate portion which is located below the rim of the basin opening, wherein furthermore, a free edge of the rim of the basin opening projects beyond the basin rim in the direction of the center of the basin prior to the completion of the entire work process.
For the purpose of simplification, reference is made below merely to a cover plate for a stainless steel sink unit with one or more basins, without the subject matter concerned being limited thereby.
Based upon the method referred to above, the procedure in respect of such cover plates has been heretofore that first the rims of the basins are connected by spot welding to the rim of the basin opening of the cover plate, in order to adjust the two parts relatively to each other and to fix them preliminarily. Thereafter, the two parts are finally connected together by a continuous roll seam welding process. This is followed by a further operating step in which the free edge which projects in the direction of the basin center, of the rim of the basin opening of the cover plate is ground off, so that a smooth transit is obtained between the basin and the cover plate. Finally, the grinding marks extending along the weld seam are removed by polishing in order to give the article consisting of the cover plate and the basin, its finished appearance.
The procedure described above is relatively complicated, time consuming and expensive in every respect. First of all, the spot-like welding connection between the cover plate and the basin requires a spot welding machine and appropriate apparatus for mutual centering of cover plate and basin. Then the roll seam welding process requires a further appropriate machine in which the unit to be treated again must be held and guided by corresponding tools. Thereupon, changeover of the article to be manufactured is required to a grinding machine which is specially arranged therefor, and finally the same applies once again for the polishing process which terminates the production. Thus, altogether four work places with the machines associated therewith as well as the associated operator for welding a basin into a cover plate must be held in readiness. Beyond this, grinding away the projecting rim of the basin opening of the cover plate causes an unnecessary loss of material.
It is also known already to produce the basin and the cover plate in one piece in the way that the basin or basins are produced by deep-drawing from the material forming the cover plate. However, this necessitates a special production method which comprises several steps and which is characterized above all by the extremely high costs of the deep-drawing tools; moreover, these deep-drawing tools are usable always for only one type or for one size, and there is thus no flexibility in respect to different types or sizes, unless a plurality of sets of these very expensive tools are kept in stock.
It is an object of the invention to simplify considerably the production method described above and thereby to render the production more economical and more rapid, the expenditure for machines and apparatus being considerably reduced at the same time and yet the possibility being provided for change-over to different types or sizes of the construction units to be produced, in a simple way.
This problem is solved by a preferred method according to the invention in that the projecting portion of the free edge of the basin opening is united by melting with the arcuate portion between the verticl wall of the basin and the horizontal rim thereof, by using the rare gas electric arc welding method without the addition of work material.
By means of these measures in accordance with the invention welding of the basin into the cover plate together with mutual centering of these two parts takes place in a single operating step to such an extent that an outwardly smoothly rounded connection between these two parts is obtained which has been found not to require as a rule any after treatment by means of polishing. Therefore, basically one work place with the associated machine and the appropriate operator is sufficient for finally producing the unit consisting of plate and basin, and automation to the fullest extent is possible with multi-machine operation as far even as fully automatic production. Moreover, the rim projecting towards the basin center, of the basin opening of the cover plate can now be utilized without loss in respect of its material, in that it is united by melting with the material of the basin to be welded, whereby the surrounding rim of the basin to be welded may be rendered narrower and a corresponding saving of material is obtained.
However, it is essential above all that compared with the method initially described, the production is not only simplified and more economical, but also is considerably increased in respect of speed.
The rare gas electric arc welding method to be particularly considered may be, to name an example only, the TIG plasma welding method (tungsten inert gas welding method with pilot arc).
Apparatus for performing the method according to the invention is particularly characterized by a machine frame having vertical guides which are connected together at the top and at the bottom by a respective cross-head, a presser plate displaceable on the guides and having fixed thereon a holder for inserting therein from above the basin to be welded, a yoke located on the upper cross-head, a support column which extends vertically downwardly from the yoke, is centrally disposed relatively to the basin holder and penetrates through an opening of the upper cross-head, a plunger for mutually centering the basin and the basin opening for the welding process, the plunger being arranged at the lower end of the support column and its peripheral contour corresponding to the inner cross-section of the basin as well as the basin opening of the frame, a presser ring which is attached to the underside of the upper cross-head, the lower end face of which is flush with the upper rim of the basin holder and the said end face of which is set back relatively to the end face of the plunger, and which surrounds the plunger equidistantly at a spacing required for the welding process, a guide track equidistantly surrounding the support column relative to the peripheral contour of the plunger above the upper cross-head, as well as at least one welding torch which is displaceable along the guide track and the torch nozzle of which is directed at a constant setting angle to the gap between the plunger and the presser ring.
This apparatus permits the basin to be welded to be inserted into the basin holder and to displace it together therewith upwardly against the presser ring with which the cover plate is already in abutment, having been centered by the plunger. Thereafter, the welding torch travels around and welds together the two parts referred to, at the same time melting away the rim projecting towards the basin center, of the basin opening of the cover plate, the radius remaining constant, whereby the entire process of connecting the cover plate and the basin is already finished. This must be followed only in rare individual cases by a polishing process, in order to remove perhaps any minor discolorations of the material caused by the welding.
The apparatus according to the invention is suitable fundamentally for continuous contours relative to which the torch is displaced substantially horizontally. Just as well, however, vertical adjustments of the torch may be produced during the welding process by appropriate configuration of the guide track and/or the arrangement of the torch on the torch carriage, for example, in order to weld a contour which narrows downwardly relatively to the upper rim of the basin to form an overflow or the like.
The constant setting of the torch in the direction of the welding location is important in respect of the setting angle relatively to the vertical as well as also to the effect that the torch is positioned always perpendicular to the tangent to the contour to be welded.
It has been found advantageous for the said apparatus that the vertical guide comprises four guide columns which connect the cross-heads together and on which the presser plate is displaceable by means of guide bushes fixed to the latter. In this case, the vertical displacement of the pressure plate, and thus the basin holder, may be effected by means of a cylinder-piston unit which is attached to the lower cross-head and the piston rod of which extends through an opening of the cross-head and is connected to the underside of the presser plate.
The basin holder may be constructed as a hollow cylinder the inner cross-section of which corresponds to the outer cross-section of the basin and the upper rim of which is engaged by the horizontal rim of the basin. Also, the basin holder may be releasably and thus interchangeably attached to the presser plate. The same applies to the plunger and the guide track as well as the presser ring, whereby the apparatus may be converted to different basin sizes to be welded by the interchange of only a few parts which do not constitute an excessive cost factor.
In a further embodiment of the apparatus for performing the method according to the invention, it may be provided that the plunger comprises along its peripheral contour a plurality of centering pins for the basin opening which project, under the effect of springs, horizontally beyond the peripheral contour, and that the centering pins may be pushed back against the effect of the springs into the peripheral contour of the plunger. Thereby, a clean centering of the basin opening of the frame may be obtained in a simple manner prior to the welding process.
Furthermore, in this context, the peripheral contour of the plunger may be formed at least partly by horizontally displaceable segments, and in this case, with the basin displaced high upon the plunger, the segments may be extendable against a spring force to their nominal position for the purpose of forming the peripheral contour of the plunger. The latter may be effected in that the segments are supported at least indirectly under the spring force on an actuating member which is vertically displaceable in the center of the guide column and the plunger and that the support surface of the actuating member is a cone. The centering pins referred to may then be disposed in the segments. These measures render it possible to adjust the basin contour additionally in a positive manner prior to the final clamping for performing the welding process.
In the further developed apparatus described above for performing the method according to the invention, it is furthermore advantageous that, starting from its secure counter-bearing at the upper cross-head for the welding process, the presser ring is vertically downwardly displaceable by a fixed amount for the force exerted upon it by the basin holder, in which case the displacement of the presser ring may occur under its inherent weight and wherein, in the rigid counter-bearing position of the presser ring, the lower edge thereof may be located above the upper edge of the centering pins and the segments. Thereby, it is possible to lift the region to be welded above the upper edge of the centering pins and the segments together with the final clamping of cover plate and basin for the welding process, and thereby to get clear of these tools.
It is advantageous that the transit between the inner cross-section and the upper edge of the basin holder comprises a bevel and thus spacing relatively to the material of the basin to be welded, in the region of the weld seam. Owing to this phasing-in of the lower tool the melting away process at the weld seam can be controlled in a particularly simple manner, because the material melts away downwardly and has been given space thereby the bevel.
Moreover, it is advantageous that the guide track comprises for the welding torch an external surrounding toothed crown, a roller chain or the like, that the pinion of the motor drive for the welding torch is in driving connection therewith, and that the motor drive as well as the welding torch are attached to a torch carriage which is guided by the guide track vertically and radially in respect of the basin contour with a constant setting angle. Also, the motor drive of the welding torch may be controllable in a stepless manner.
Furthermore, it is advantageous that the radial guide for the welding torch consists of a surrounding rail of the guide track which extends vertically upwardly, and such a rail which extends vertically upwardly, and such a rail which extends vertically downwardly, that the torch carriage is guided at the upper rail on the outside by the pinion of the drive and on the inside by a securely adjustable roller, and that the torch carriage is guided at the lower rail on the outside by a securely adjustable roller and on the inside by radially resilient rollers which permit an adjustment of the torch corresponding to the basin radii.
In another constructional form, the torch carriage is radially and vertically guided by a surrounding vertical rail, the torch carriage is guided at the upper end of the rail on the inside by a securely adjustable roller and vertically by two downwardly resiliently mounted rollers as well as at the lower end of the rail on the outside by a securely adjustable roller and on the inside by two resiliently mounted rollers as well as vertically by two support rollers with a circumferential groove embracing the lower end of the rail, the support rollers are commonly axially displaceably mounted in a bogic which is rotatable about a vertical axis on the torch carriage, the inwardly located substantially radial edge of the circumferential groove of the support rollers is bevelled in the manner of a rail wheel, and the torch is connected to the rotary bogie or the axis of rotation thereof.
Finally, it has been found to be particularly advantageous that always two displaceable torches are provided which are displaceable through an arc of 180.degree.. Thereby, the welding speed is doubled, in that two torches travel substantially through only half the arc to be welded altogether and are then stopped. After the next following workpiece has been inserted, the torches can then be returned in the welding work process.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.